This chapter discusses the most widely used physical sterilization techniques and includes the use of moist heat, dry heat, and radiation. High-temperature steam (or steam under pressure) is the most widely used sterilization method. Steam is simply a gas that is produced by the heating of water and therefore can be explained by the gas laws that consider four variables: volume, temperature, pressure, and the amount of gas. Efficient air removal is essential to ensure steam sterilization, as air prevents the penetration of steam and leaves cold spots within the chamber/load that will not be adequately sterilized. Dry-heat sterilization methods include sterilization ovens and incineration. Incineration is essentially burning to ashes, which can be performed by passing material through a naked flame (for example, in microbiological manipulations by flaming) or in much larger scale applications in kilns or furnaces. For radiation sterilization, only high-energy or ionizing-radiation sources are utilized, due to their greater penetration and antimicrobial efficacy. Filtration methods can be used for sterilization of gas (such as air) and liquids, including water. The chapter also discusses developing methods, including plasma, pulsed-light applications, supercritical fluids, and pulsed electric fields.

A steam sterilizer. Sterilizers are available in a variety of sizes and shapes, depending on the application. In addition, the steam sterilization process can be conducted as an intrinsic process of some manufacturing/industrial equipment, which can be routinely sterilized without being disassembled.

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FIGURE 5.2

A steam sterilizer. Sterilizers are available in a variety of sizes and shapes, depending on the application. In addition, the steam sterilization process can be conducted as an intrinsic process of some manufacturing/industrial equipment, which can be routinely sterilized without being disassembled.

The Bowie-Dick test, a method of testing the steam penetration and air removal capabilities of a vacuum sterilizer. Single-use test packs are shown at the top; they consist of a chemical indicator at the center of the test pack, which changes color on exposure to the correct combination of time, temperature, and steam. An unused indicator and one failing and one passing chemical indicator results are shown from left to right at the bottom.

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FIGURE 5.7

The Bowie-Dick test, a method of testing the steam penetration and air removal capabilities of a vacuum sterilizer. Single-use test packs are shown at the top; they consist of a chemical indicator at the center of the test pack, which changes color on exposure to the correct combination of time, temperature, and steam. An unused indicator and one failing and one passing chemical indicator results are shown from left to right at the bottom.

The generation of X rays. Electrons are shown being generated from the cathode and reacting with atoms at the anode to produce electrons via two mechanisms discussed in the text (brehmsstrahlung [A] and direct collision [B]).

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FIGURE 5.13

The generation of X rays. Electrons are shown being generated from the cathode and reacting with atoms at the anode to produce electrons via two mechanisms discussed in the text (brehmsstrahlung [A] and direct collision [B]).

The relationship between solid, liquid, gas, and supercritical fluid states for a substance. As the temperature and pressure increase, the substance can exist in each state. Above the critical temperature (Tc) and pressure (Pc), the substance demonstrates combined properties of a liquid and gas and is known as a supercritical fluid.

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FIGURE 5.20

The relationship between solid, liquid, gas, and supercritical fluid states for a substance. As the temperature and pressure increase, the substance can exist in each state. Above the critical temperature (Tc) and pressure (Pc), the substance demonstrates combined properties of a liquid and gas and is known as a supercritical fluid.

References

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1. Association for the Advancement of Medical Instrumentation.2005.Sterilization. Part 1: Sterilization in Health Care Facilities.Association for the Advancement of Medical Instrumentation,Arlington, Va.

2. Association for the Advancement of Medical Instrumentation.2005.Sterilization. Part 2: Sterilization Equipment.Association for the Advancement of Medical Instrumentation,Arlington, Va.

3. Association for the Advancement of Medical Instrumentation.2005.Sterilization. Part 3: Industrial Process Control.Association for the Advancement of Medical Instrumentation,Arlington, Va.